SA Friday
01-09-2016, 10:10
Once you’ve got past the choice of buying a factory built AR and have decided to build an AR, figuring out where to start and what parts you should use are the next decisions to make. There are four parts that you should invest into first, and they are also the most critical for a good gun. The lower receiver, upper receiver, barrel, and bolt/bolt carrier group (lets consider these one part for sake of discussion). If you try to save money in these parts, your overall build will suffer.
The barrel and bolt are literally the heart of the gun and regardless of the other parts literally do the actual shooting mechanically. These parts are controlling an explosion. Think about that for a second, these two parts are taking 55,000 psi of deflagrated gas pressure every single time you pull the trigger. I am still amazed just how many times I see people try to save a buck on these parts and then suffer the ramifications of bad tolerances. I wrote a thread about barrels, it goes into detail that I will skip here.
Bolts/bolt carrier groups (BCG) are critical for cycling. I look for bolts that were magnetic particle inspected (MPI, marked on the bolt). This doesn’t change the manufacture process or material composition, but ensures there aren’t any spots of potential failure in the material of the bolt. Obviously, this doesn’t guarantee it won’t fail, but I have seen more non-marked bolts fail than marked. Other potential testing is high pressure testing (HP or HPI, marked on the bolt). I’m not convinced that HP testing is necessary or actually guarantees a better product. It doesn’t make it worse, but I can’t say it’s a make or break test.
Bolt carrier groups come in four different configurations. The most common is the M4/M16 cut BCG. They have equal cuts in the back of the BCG area. The top cut is in the same length at the bottom cut. AR15 bolts are basically the same but the bottom cut is further back than the top cut. The third is the half-moon bolt. Its bottom cut basically goes all the way back and the removes the bottom to make it look like a half moon from the rear view. Last, you have custom specialized cut BCGs. The most common of these are lightened BCG and they have cuts, holes, and amputated parts in every imaginable configuration. The biggest reason for the different BCGs is manufacturers making the AR and half moon BCGs to make the guns more compliant to anti-machinegun gun control measures. The most prominent influence was the Brady Act (1994). As the bottom cut in the BCG works in coordination with the auto sear, cutting the bottom cut in a BCG stops it from being able to work in an auto gun. The half-moon BCG does the same thing and was the horrific idea of Colt. As you can tell, I don’t approve of the half moon BCGs. They suck and can get caught up in the lower due to the bottom cut. I don’t mind the AR BCG, but I prefer the M4/M16 BCG to it also.
What about specialized bolts? Well, here is where it can get complicated. Mass and spring weight is used to get ARs to cycle with proper timing. Too fast or too slow can cause excessive wear, parts failure, jams, cats and dogs living together… all kinds of bad shit. In general, a slightly slower cycling gas system works better than too fast. As long as it still will lock the bolt back, it’s not too slow. M4/M16 BCGs being heavier have a tendency to run a little better. So why do they make lightened BCGs of every possible kind? Because of reciprocating mass. The light version explanation is the less weight bouncing back and forth during the firing cycle, the less recoil and movement in the gun. Lots of shooters, especially competition shooters, run highly specialized gear to maximize the speed and ease of shooting. It does work, but these are guns typically running reloaded ammo made for the modifications and are constantly re-tuned to run reliably. In the end, these typically cause issues more than solve issues for the average shooter. The average shooter is best served with a basic M4/16 BCG.
There are a couple of new coatings on bolts and BCGs, and even in uppers. Nickel boron (NiB) and nickel Teflon (NP3) are the two most common. I don’t have a lot of experience with NP3, but from what I’ve seen from NiB, it’s worth the extra money. A good bolt/BCG is running around $140. The same coated in NiB is about $180. The NiBs clearly run with considerably less friction. Some even run these without any additional lubricant. They are holding up to this use. They can be damaged from excessive exposure to cleaning with very basic pH cleaners. Short of that, they do run better.
Last thing about BCGs, THE GAS KEY MUST BE STAKED. I read about how it doesn’t matter all the time. Bullshit! If it isn’t staked, move along. Lock-tite won’t cut it. This thing is taking a 15,000-20,000 psi hit searing hot gas every time a round is shot. Then it’s cycling back and forth and has to cleanly slip over the gas tube. If it’s loose, you have an instant club.
Upper and lower receivers are fairly inexpensive even for really good ones. I see many cut this corner regularly too. One has to ask themselves why a company is selling a $35 lower and the reputable companies are a $100 to $135. Some of this is usually more machining and engraving. Lets face it, it costs time and money to engrave a zombie face on a lower. It’s not $100 more engraving though. It’s better material and better tolerances. Best example I can give is this; if the safety selector hole is drilled 1mm lower than it should be, it then presses on the trigger which then pushes up on the hammer and stops you from being able to install the hammer. Sure, I can custom cut parts to work, but damn. Why should I custom cut a trigger for a part that could have just as easily been in spec and now you are limited to only that trigger. Spend the money.
Uppers and lowers come in aluminum, polymer, and composites. Keep it simple, stick with the aluminum. They are stronger for the weight. I’ve seen to many of the polymers and composites have problems or crack. Aluminum uppers and lowers can be either forged or milled. Forged are thinner and lighter and equal or more strong than milled. Milled are cleaner looking with sharper edges and more variety. If you are just starting out, stick with a forged from a good company and you really can’t go wrong. If you want to save a few bucks and are planning on putting a scratch or two in the gun anyway, look into blem uppers and lowers from good companies. It’s pretty rare to actually be able to see a blem so bad it’s clearly an actual blem part. If your build is going straight for the cool-factor, milled are IMO much better looking. You might run into parts that won’t work with the milled though, they are not mil-spec. Almost all uppers and lowers are ionized finished. Many companies are now painting theirs. Either will work. Painted is usually a little more cost.
This is where to start in your build. Don’t skimp on them. You are better off spending an extra $100 on these four parts and saving on the handguard or stock. I am a huge advocate of the “cry once” principal, but if you are on a budget, still don’t cut corners going cheap on these.
The barrel and bolt are literally the heart of the gun and regardless of the other parts literally do the actual shooting mechanically. These parts are controlling an explosion. Think about that for a second, these two parts are taking 55,000 psi of deflagrated gas pressure every single time you pull the trigger. I am still amazed just how many times I see people try to save a buck on these parts and then suffer the ramifications of bad tolerances. I wrote a thread about barrels, it goes into detail that I will skip here.
Bolts/bolt carrier groups (BCG) are critical for cycling. I look for bolts that were magnetic particle inspected (MPI, marked on the bolt). This doesn’t change the manufacture process or material composition, but ensures there aren’t any spots of potential failure in the material of the bolt. Obviously, this doesn’t guarantee it won’t fail, but I have seen more non-marked bolts fail than marked. Other potential testing is high pressure testing (HP or HPI, marked on the bolt). I’m not convinced that HP testing is necessary or actually guarantees a better product. It doesn’t make it worse, but I can’t say it’s a make or break test.
Bolt carrier groups come in four different configurations. The most common is the M4/M16 cut BCG. They have equal cuts in the back of the BCG area. The top cut is in the same length at the bottom cut. AR15 bolts are basically the same but the bottom cut is further back than the top cut. The third is the half-moon bolt. Its bottom cut basically goes all the way back and the removes the bottom to make it look like a half moon from the rear view. Last, you have custom specialized cut BCGs. The most common of these are lightened BCG and they have cuts, holes, and amputated parts in every imaginable configuration. The biggest reason for the different BCGs is manufacturers making the AR and half moon BCGs to make the guns more compliant to anti-machinegun gun control measures. The most prominent influence was the Brady Act (1994). As the bottom cut in the BCG works in coordination with the auto sear, cutting the bottom cut in a BCG stops it from being able to work in an auto gun. The half-moon BCG does the same thing and was the horrific idea of Colt. As you can tell, I don’t approve of the half moon BCGs. They suck and can get caught up in the lower due to the bottom cut. I don’t mind the AR BCG, but I prefer the M4/M16 BCG to it also.
What about specialized bolts? Well, here is where it can get complicated. Mass and spring weight is used to get ARs to cycle with proper timing. Too fast or too slow can cause excessive wear, parts failure, jams, cats and dogs living together… all kinds of bad shit. In general, a slightly slower cycling gas system works better than too fast. As long as it still will lock the bolt back, it’s not too slow. M4/M16 BCGs being heavier have a tendency to run a little better. So why do they make lightened BCGs of every possible kind? Because of reciprocating mass. The light version explanation is the less weight bouncing back and forth during the firing cycle, the less recoil and movement in the gun. Lots of shooters, especially competition shooters, run highly specialized gear to maximize the speed and ease of shooting. It does work, but these are guns typically running reloaded ammo made for the modifications and are constantly re-tuned to run reliably. In the end, these typically cause issues more than solve issues for the average shooter. The average shooter is best served with a basic M4/16 BCG.
There are a couple of new coatings on bolts and BCGs, and even in uppers. Nickel boron (NiB) and nickel Teflon (NP3) are the two most common. I don’t have a lot of experience with NP3, but from what I’ve seen from NiB, it’s worth the extra money. A good bolt/BCG is running around $140. The same coated in NiB is about $180. The NiBs clearly run with considerably less friction. Some even run these without any additional lubricant. They are holding up to this use. They can be damaged from excessive exposure to cleaning with very basic pH cleaners. Short of that, they do run better.
Last thing about BCGs, THE GAS KEY MUST BE STAKED. I read about how it doesn’t matter all the time. Bullshit! If it isn’t staked, move along. Lock-tite won’t cut it. This thing is taking a 15,000-20,000 psi hit searing hot gas every time a round is shot. Then it’s cycling back and forth and has to cleanly slip over the gas tube. If it’s loose, you have an instant club.
Upper and lower receivers are fairly inexpensive even for really good ones. I see many cut this corner regularly too. One has to ask themselves why a company is selling a $35 lower and the reputable companies are a $100 to $135. Some of this is usually more machining and engraving. Lets face it, it costs time and money to engrave a zombie face on a lower. It’s not $100 more engraving though. It’s better material and better tolerances. Best example I can give is this; if the safety selector hole is drilled 1mm lower than it should be, it then presses on the trigger which then pushes up on the hammer and stops you from being able to install the hammer. Sure, I can custom cut parts to work, but damn. Why should I custom cut a trigger for a part that could have just as easily been in spec and now you are limited to only that trigger. Spend the money.
Uppers and lowers come in aluminum, polymer, and composites. Keep it simple, stick with the aluminum. They are stronger for the weight. I’ve seen to many of the polymers and composites have problems or crack. Aluminum uppers and lowers can be either forged or milled. Forged are thinner and lighter and equal or more strong than milled. Milled are cleaner looking with sharper edges and more variety. If you are just starting out, stick with a forged from a good company and you really can’t go wrong. If you want to save a few bucks and are planning on putting a scratch or two in the gun anyway, look into blem uppers and lowers from good companies. It’s pretty rare to actually be able to see a blem so bad it’s clearly an actual blem part. If your build is going straight for the cool-factor, milled are IMO much better looking. You might run into parts that won’t work with the milled though, they are not mil-spec. Almost all uppers and lowers are ionized finished. Many companies are now painting theirs. Either will work. Painted is usually a little more cost.
This is where to start in your build. Don’t skimp on them. You are better off spending an extra $100 on these four parts and saving on the handguard or stock. I am a huge advocate of the “cry once” principal, but if you are on a budget, still don’t cut corners going cheap on these.